HK 730 making noises...

RockysDad · 23rd December 2005, 11:12 PM

I have a vintage Harmon Kardon 730 receiver that I am trouble with crackling noise out of the right output. Its not in the amp section because there is a jumper that can separate it from the preamp and testing the amp by itself is clean. The power supply seems to be okay since the power amp is fine. Therefore it must be the preamp. I think... Other clues are that its not volume or sourse dependent. Its just sort of there, sometimes worst them other times.

Just recently, with the power "off" the right speaker started to crackle and pop loudly for no apparent reason. I am trying to figure that one out. I mean the power was off and yet there was crackling and popping noises being outputed. Very strange. It seems that maybe a cap is being discharged somehow somewhere but the power amp has to be powered up doesn't it? So I am looking for ideas on where to start looking. I do have a schematic but am out of ideas on where to look. I did change all the biggger caps in the power supply section and all the caps in the pre-amp section. It still crackles some but not as bad.

Bad switch maybe, power supply for the pre-amp section? I wish I had a scope but don't. What else can I do?

TIA...

amplifierguru · 23rd December 2005, 11:18 PM

Hi Rockysdad,

It's old so PS electro's are sus.

Do L and R channels of the preamp section share the same power supply? If not you could swap the C's to see if it changes L <->R.

Cheers,
Greg

jblmar · 24th December 2005, 12:45 AM

Could be an electrolytic cap in the PS or a bad diode. Some designs used diodes for a quick discharge.
Ron

23rd December 2005, 11:12 PM	#1
RockysDad diyAudio Member Join Date: Sep 2003 Location: Bay Area, CA	HK 730 making noises... I have a vintage Harmon Kardon 730 receiver that I am trouble with crackling noise out of the right output. Its not in the amp section because there is a jumper that can separate it from the preamp and testing the amp by itself is clean. The power supply seems to be okay since the power amp is fine. Therefore it must be the preamp. I think... Other clues are that its not volume or sourse dependent. Its just sort of there, sometimes worst them other times. Just recently, with the power "off" the right speaker started to crackle and pop loudly for no apparent reason. I am trying to figure that one out. I mean the power was off and yet there was crackling and popping noises being outputed. Very strange. It seems that maybe a cap is being discharged somehow somewhere but the power amp has to be powered up doesn't it? So I am looking for ideas on where to start looking. I do have a schematic but am out of ideas on where to look. I did change all the biggger caps in the power supply section and all the caps in the pre-amp section. It still crackles some but not as bad. Bad switch maybe, power supply for the pre-amp section? I wish I had a scope but don't. What else can I do? TIA...

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23rd December 2005, 11:18 PM	#2
amplifierguru Account Disabled Join Date: Aug 2004 Location: Earth	Hi Rockysdad, It's old so PS electro's are sus. Do L and R channels of the preamp section share the same power supply? If not you could swap the C's to see if it changes L <->R. Cheers, Greg

24th December 2005, 12:45 AM	#3
jblmar diyAudio Member Join Date: Dec 2005 Location: Brooklyn, New York	Could be an electrolytic cap in the PS or a bad diode. Some designs used diodes for a quick discharge. Ron

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